The prominent appearance of lines and wrinkles on the skin is due to optical geometry. In terms of a person's skin, diffuse reflectance occurs readily, but to differing degrees. When the surface of the skin is smooth, light is absorbed, reflected and scattered off the skin surface and is observed as a color according to how much light is absorbed and scattered. To the contrary, however, the intensity of the light reflected back to the observer's eye from wrinkles on the skin surface is less than that from normal skin and, as a result, the eye will perceive the wrinkled skin regions as darker and thus more noticeable. An increase in the degree of diffuse reflectance would help to modify the perceived appearance of wrinkled skin since the ability to scatter light in greater directions would prevent the eye from clearly viewing the skin surface as it actually exists.
A number of methods have been developed to reduce wrinkles and minimize fine lines. Some of these methods include active ingredients such as antioxidants; agents that act by neurotransmission inhibition in nerve cells such as botulinum toxin (Botox™) (Allergan, Irvine, Calif.), thereby relaxing contracted muscles; agents that accelerate the cell renewal process such as hydroxy and fruit acids like retinoic acid; emollients such as shea butter; skin plumpers such as hyaluronic acid; fillers such as collagen; light-diffusing pigments and microspheres which create the illusion that wrinkles have disappeared. Other methods have been developed to reduce the appearance of pores, skin surface unevenness and imperfections and the like. Some of these methods include skin lightening agents, which fill and camouflage the skin.
The optical reduction of wrinkles can also be achieved through the light diffusing properties of the applied particles to the surface of the skin. At the margins and in the creases of wrinkles, particles that scatter and thus diffuse light away minimize the depressions in the skin. To the observer, the wrinkles appear blurred, hence the terms “soft focus effect” or “blurring effect.” In the past, the blurring effect was based on the diffuse reflection of spherical particles such as microspheres and fibers. One such composition is described by Nakamura, N. et al., “Blurring of Wrinkles Through Control of Optical Properties”, XIVth I.F.S.C.C. Congress, Barcelona, Spain, 1986.
Unfortunately, some of these methods do not have an immediate response, requiring days and weeks of continued use to see any beneficial effects. Others are invasive, requiring injections, patient discomfort, and may entail redness, swelling and other side effects. Furthermore, many cosmetic foundations and make-up actually accentuate wrinkles and fine lines due to migration of the pigments into the wrinkle crevices. Other products cover skin imperfections creating an unnatural, caked-on appearance. Yet others, such as mica, reflect light rather than diffuse and scatter light, thereby resulting in an unnatural shiny appearance.
Of particular interest, one known method that has been developed to reduce wrinkles and minimize fine lines employs optically diffusing pigments that are commonly used to scatter the incident light more evenly across the surface of the skin in order to minimize the quantity of light lost in a wrinkle, thus making wrinkles appear less visible. One of the most commonly used optically diffusing pigments is titanium dioxide, due to its reflective nature. As a result, the wrinkles and fine lines are masked and not highlighted. However, this method has been found to be undesirable because titanium dioxide (TiO2) particles generally exhibit indices of refraction vastly different from those commonly found in cosmetic formulations. Thus, use of TiO2 particles produce target cosmetic formulation that are too opaque for sufficient transmittance of light to occur. As a result, the formulation at conventional TiO2 concentrations (˜10-15%) invariably appear white when applied to a user's skin, rather than permitting optical blurring with a skin-tone coloration. Avoidance of such a white coloration is therefore required for proper cosmetic benefits to be achieved.
The need exists for alternative methods of providing a natural and smooth appearance to the skin with visible reduction in wrinkles, fine lines, pores and skin imperfections and yet overcome the problems associated with previous methods and compositions. Achieving these beneficial objectives would represent a significant advancement in the cosmetic art.
The incorporation of inorganic nanoscale particles into a polymeric matrix is known for various industrial uses to provide clear coatings, for example, mobile phones or skies. However, there remains a need for a novel way of imparting blurring while preserving the natural look of a foundation on the skin by reducing the appearance of wrinkles, fine lines, pores and skin imperfections.